Such a laser device and a production method therefore is known from U.S. Pat. No. 6,954,479, the content of which is incorporated herewith in the present description by reference. An optically pumped surface-emitting semiconductor laser device comprising an amplifier region as vertical emitter region and at least one edge-emitting semiconductor laser as pump radiation source is described. The vertical emitter region and the pump radiation source are grown epitaxially on a common substrate. This makes it possible to achieve a space-saving monolithically integrated arrangement of vertical emitter region and pump radiation sources.
A high pumping efficiency, and thus a high output power of the vertical emitter, is achieved if the wavelength of the pump radiation source is shorter than the wavelength of the radiation emitted by the vertical emitter. This can be achieved, for example, by means of different compositions of the materials of the radiation-emitting pump or vertical emitter layer or by different dimensioning of these layers.
A typical production approach for such a semiconductor laser device is to epitaxially grow the layers for the vertical emitter region initially over a large area on a substrate. Subsequently, these layers are selectively etched away again in the lateral regions which are provided for the pump radiation sources. In a second step of epitaxy, the layers of the pump radiation sources are then finally grown epitaxially in these regions.
Such a two-step epitaxial process is disadvantageous for a number of reasons. In the transition region between pump radiation sources and vertical emitter region, it is difficult to avoid grain boundaries and an increased density of defects which leads to optical absorption losses at this point. Furthermore, the edge of the vertical emitter region can influence the growth mode of the layers of the pump radiation sources in the transition region which can result in a disadvantageous deviation of the layer thicknesses in this transition region. In addition, the two-step epitaxial process is associated with high production expenditure.
From Gerhold et al., IEEE Journal of Quantum Electronics, Volume 34, No. 3, 1998, pages 506-511, an optically pumped semiconductor laser device produced in a one-step epitaxy is known. Vertical emitter region and pump radiation sources have a common active layer with a quantum well structure. In the region used as pump radiation source, the quantum well structure is intermixed with impurity atoms which leads to the generation of radiation having a shorter wavelength in this region than in the vertical emitter region (IILD—impurity induced layer disordering). However, the method of intermixing with impurity atoms only allows small variations of the wavelength and is also accompanied by the risk that the effectiveness of the radiation emission and thus the pump efficiency will drop.
A general problem with optically pumped semiconductor laser devices which are produced in a one-step epitaxy is represented by the fact that the layer structure of vertical emitter region and pump radiation sources is initially identical. Ideally, in operation, a radiation field expanding laterally should only be generated in the area of the pump radiation sources and in the vertical emitter region only a radiation field expanding in the vertical direction should be generated. Vertically propagating modes in the region of the pump radiation sources reduce the pump radiation power generated. Analogously, laterally expanding radiation modes generated in the vertical emitter region reduce the population inversion and thus the pump efficiency. An efficiently operating semiconductor laser device of said type thus presupposes that the balance between pump layer and vertical emitter layer is cancelled, i.e. that pump layer and vertical emitter layer are no longer equivalent.